The invention relates to an apparatus and method for processing a semiconductor, and more specifically, relates to an apparatus and method for surface treating a semiconductor wafer in preparation for an in-line monitoring procedure.
Operation of an integrated circuit (IC) depends on the electrical properties of materials of which the circuit is formed. Therefore, by monitoring selected electrical properties of these materials in the course of an IC fabrication, an effective control over the manufacturing process can be accomplished. Since modern ICs are typically formed in the shallow region below the surface of a semiconductor wafer, critical electrical properties are directly or indirectly related to the condition of the surface region of the semiconductor wafer. Surface properties of a semiconductor wafer can be monitored during IC fabrication through in-line monitoring procedures such as described in U.S. Pat. Nos. 4,544,887 and 5,661,408.
The in-line monitoring procedure permits surface properties of a semiconductor wafer to be measured without contacting the wafer surface, so that the surface properties are not affected by the measurement itself However, unlike conventional methods of electrical characterization in which contaminant ions and molecules from the ambient environment do not significantly affect the measurements due to formation of a permanent contact on the surface of the wafer, non-contact measurements may not provide accurate information about the wafer. This is because contaminant ions and molecules from the ambient environment may adsorb on the surface of the wafer during transportation and storage, changing surface properties of the wafer. Consequently, it may-be difficult to obtain accurate information about the surface properties of the semiconductors with the in-line monitoring procedures unless the semiconductors are surface treated prior to being measured.
According to one known method, a p-type silicon wafer is surface treated by being immersed in dilute hydrofluoric acid, rinsed with deionized water and dried in order to restore an inversion condition. A width of surface depletion layer measured under an inversion condition provides net doping concentration in the sub-surface region. Existing surface preparation steps, however, are typically not integrated with subsequent measurement steps. In addition, existing processing and monitoring methods are not capable of establishing the surface condition of a wafer by means of a simple treatment in ambient environment at atmospheric pressure as needed to carry out a specific electrical measurement.
Therefore, there is a need for an apparatus and method which determine selected electrical parameters of semiconductor wafers representing the outcome of individual processing steps, independent of the ambient atmosphere in which the wafers are stored or transported.
It is an object of the invention to provide a surface treatment apparatus and method, which reduce the affect of ambient environment, in which a wafer is transported or stored between processing steps, on the wafer surface condition. It is another object of the invention to provide a surface treatment apparatus and method which can be integrated with an in-line monitoring apparatus and method.
In one aspect, the invention features a method for in-line, real-time monitoring of a semiconductor wafer. According to the method, a plurality of electron-hole pairs are created near a surface of the wafer and the wafer is heated to substantially desorb any of a plurality of contaminant ions and molecules adsorbed on the surface of the wafer. In one embodiment, the plurality of electron-hole pairs are created by illuminating the wafer with a radiation of photon energy sufficient to create the plurality of electron-hole pairs. In another embodiment, the wafer is heated by illuminating the wafer with a near infrared radiation. In still another embodiment, the wafer is a p-type wafer and heating and illuminating the p-type wafer restores an inversion layer on the surface of the p-type wafer.
In another aspect, the invention features an apparatus for surface treating a semiconductor wafer. The apparatus includes a surface treatment chamber and a source of radiation, which illuminates a semiconductor wafer disposed inside the chamber with radiation sufficient to create a plurality of electron-hole pairs near a surface of the wafer and to desorb any of a plurality of ions and molecules adsorbed on the surface of the wafer. In one embodiment, the surface treatment chamber is integrated with an in-line, real-time testing apparatus such that a surface photovoltage of the wafer can be measured after the wafer has been surface treated. In another embodiment, the apparatus further comprises a power control circuitry for controlling an intensity of radiation from the radiation source.